The present invention relates to a device for monitoring and/or measuring parameters of a running, thread-like or wire-like test material, having a measuring gap which is provided for the passage of the test material and on each of the two side walls of which is provided a measuring electrode forming part of a capacitive measuring element.
There are now millions of devices of this kind which are based on the capacitive measuring principle, such as so-called electronic yarn clearers, on the one hand, and uniformity testers on the other hand. The electronic yarn clearers, such as the USTER AUTOMATIC type from Zellweger Uster AG, serve to detect troublesome yarn defects, including, for example, short thickenings, thinnings and frequent thickenings and thinnings (Moire). Uniformity testers such as the USTER TESTER from Zellweger Uster AG (USTER is a registered trademark of Zellweger Uster AG) serve to detect and analyze fluctuations in the weight per unit length of slivers, rovings and yarns.
Due to its high measuring accuracy and its constant sensitivity for many years, the capacitive measuring principle has become very widespread. In addition to the devices based on this principle, optical measuring heads are also used, with which the diameter of the test material can be determined. These optical measuring heads are used in particular when capacitive measuring heads cannot be employed. This is the case, for example, with the testing of electrically conductive yarns.
Irrespective of the type of measuring principle used, the measuring heads are dependent to a certain extent, due to their principle of operation and their construction, on extraneous influences, such as, for example, moisture, shape of the yarn cross-section, position of dependency, influence of the material, etc., which cannot be eliminated or reduced using the technology available although there would be great interest in doing so. A further, as yet unsolved problem is a universal measuring head usable for all types of yarns with all the advantages of the capacitive measuring principle. Finally, with increasing automation, it would also be desirable if a type of self-checking measuring head were available.